Fluid jet printing device

ABSTRACT

The present invention relates to a fluid jet printing device A to U having an inlet 14, an outlet nozzle 13 and a valve 3, 5 located between the inlet and the outlet. The valve comprises a movable actuation member 3 cooperating with a valve seat. 
     For enhancing the drop generation frequency, a diaphragm-like partition wall PW is arranged between the inlet and the outlet. Said partition wall includes the valve seat VS.

The present invention relates to a fluid jet printing device.

Fluid jet printing devices having an inlet which is connected to asource for feeding ink or another printing fluid to the device, furthercomprising an outlet formed by a nozzle for forming drops and a valvelocated between the inlet and the outlet are commonly known in the artand commercially available as so-called ink jet printers. Printers ofthis kind or a similar kind are known from the following referenceswhich are cited as a technical background with respect to the presentinvention: EP-A 83 877, FR-A 23 38 089, GB-A 20 03 429, DE-A 29 05 063and FR-A 24 98 988. Fluid jet printing devices of the kind mentionedabove include a solenoid valve having a coil and a movable actuationmember or body cooperating with a valve seat, said valve seat beinglocated between the inlet and the outlet. The valve seat of prior artfluid jet printing devices is formed as a part of the valve housinglocated opposite to the actuation member.

As known per se in the art, characters are generated by fluid jetprinters by ejecting a plurality of fluid drops for forming dots whichtogether define the desired character. The fluid drops are generated bya number of jet nozzles of a number of fluid jet printing devicesforming together a fluid printer. The jet nozzles are arranged in aside-by-side fashion. The nozzles are supplied from a common source forfeeding fluid having a predetermined pressure over a plurality ofsolenoid valves, one for each nozzle, said valves being controlled by aprogrammable character generator which is connected to each of saidsolenoid valves. For complying with today's requirements concerningfluid jet printers, high actuation frequencies or drop generation ratesare necessary. In case of generating characters by fluid jet printingdevices forming drops having a diameter of 0.2 mm on the paper orregistration medium, seven fluid jet nozzles are required in aside-by-side arrangement for forming a character height of approximately1.5 mm. In case of a speed of the registration medium, e.g. the paperwhich is moved past the printing nozzles, of two meters per second, thenecessary valve control frequency must be in the range of 2 kHz whenaccepting a dot size of approximately 1 mm. When considering thesefigures, it will be clear that a high drop-forming frequency is ofutmost importance for high speed/high quality-printers. None of theprior art fluid jet printing devices fulfil the requirements asindicated above.

In view of this state of art, the present invention is based on thetechnical task of how to provide a fluid jet printing device having anincreased drop-generation frequency.

This technical task is solved by a fluid jet printing device of theabove-mentioned type having a diaphragm-like partition wall separatingthe inlet from the outlet and including the valve seat.

The flexible-diaphragm-like partition wall is bent when actuating themovable actuation member of the valve. The bending of the flexiblediaphragm-like partition wall can be caused by the physical contactbetween the movable actuation member at the very moment of closing thevalve seat or can alternatively be caused by a pressure-wave generatedby the actuation member and bending the partition wall located oppositethereto without necessarily requiring any physical contact between theactuation member and the diaphragm-like partition wall. The bending ofthe diaphragm-like partition wall towards the outlet of the valveresults in a pressure-peak shortly before or at the very moment ofclosing of the valve. The pulse-like increasing of the pressure of thefluid at the outlet side of the valve assists and promotes thegeneration of drops by the jet nozzle, these drops do not have anytendency of flowing together during their flight towards the paper orregistration medium.

Advantageous embodiments of the fluid jet printing device in accordancewith the present invention as well as a printer comprising a pluralityof these printing devices are defined in the subclaims.

Hereinafter, preferred embodiments in accordance with the presentinvention will be described with reference to the attached drawings, inwhich:

FIG. 1 shows a cut-view of an embodiment of the fluid jet printingdevice in accordance with the present invention;

FIG. 2 shows a detail of the embodiment in accordance with FIG. 1; and

FIG. 3 shows the arrangement of 3×7 fluid jet printing devices forming afluid printer.

The fluid jet printing device shown in FIG. 1 includes a first and asecond mounting plate 1a, 1b to which a valve housing is fitted andsecured. The valve housing consists in a valve body 3 of soft-magneticmaterial, preferably of a teflon-coated cobalt or nickel-iron alloy,which is movably journalled in a coil support 4, preferably ofglass-ceramic material, by means of a magnetic coil 5 connected to acharacter generation circuit (not shown here) by means of electricalconnection wires 6a, 6b. The lowermost end of the valve body 3 includesa sealing plate 7, preferably consisting of elastomeric material. Anarmature 8 and a rod-like distance member 9, fitted between the firstand second mounting plate 1a, 1b form a magnetic circuit together withthe valve body 3.

The first mounting plate 1a is attached to a first duct plate 10a, whichin turn is connected to a second duct plate 10b via an interjacentsealing--or stuffing foil 11 preferably consisting of nylon plasticmaterial. A fluid duct 12 is provided in the second duct plate 10b. Saidfluid duct 12 extends to a jet nozzle 13. A registration medium,preferably a registration paper, is arranged to be moved past said jetnozzle 13 for a relative movement with respect thereto. The fluid F' issupplied from a source of pressure-fluid to the inlet 14 and is fed viaa duct 15 in the first duct plate 10a into a first chamber C₁ containingthe fluid having a pressure corresonding to the pressure of the fluid ofsaid source (not shown here).

The first chamber C₁ is separated from a second chamber C₂ arranged inthe second duct plate 10b by a diaphragm-like partition wall PW made ofa thin, foil-like material, preferably stainless steel. The secondchamber C₂ conducts the fluid F" via the duct 12 towards the outletopening defined by the nozzle 13 having a diameter which is preferablyin the range of 0.05 to 0.1 mm. The fluid in the first chamber C₁ has apressure which is chosen to be in the range of 1 to 3 bars. The fluid inthe second chamber C₂ has an atmospheric pressure in the closed positionof the valve body 3 since the fluid duct system on this side of thepartition wall PW is open towards the ambient air through the nozzle 13.The partition wall PW, which is fitted between the sealing or stuffingfoil 11 and the second duct plate 10b has a cone-shaped valve seat VSdefining a hole passage MP (medium passage) for the fluid. The valveseat VS coacts with the sealing plate 7 of the valve body 3.

The valve seat VS having a hole passage MP is manufactured by embossingor punching a hole in the foil material forming the partition wall PW.The foil material consisting of stainless steel has a thickness in therange of 0.01 to 0.3 mm, preferably in the range of 0.02 to 0.05 mm. Bypunching or embossing a hole in the foil material, a collar orcone-shaped valve seat is generated. The small thickness of the foilcontributes to a minimal capillary effect although the hole diameter isas small as 0.05 to 0.1 mm. The minimal capillary effect results in asmall pressure difference between the inlet and the outlet.

The partition wall can be moved or bent like a diaphragm or membrane dueto its small thickness.

The second chamber C₂ has a very small extension in the direction of themovement of the valve body 3. A permanent magnet PM is mounted withrespect to the second duct plate 10b immediately below the secondchamber C₂. The permanent magnet is made of a steel alloy which isavailable under the tradename "SAMARIUM" having adapted magneticproperties and guaranteeing a high field strength. The permanent magnetPM is mounted in an adjustable screw 17, by which the position of themagnet relative to the valve seat VS and with respect to the valve body3 in contact with the valve seat 3 in the closed resting position of thevalve can be changed. Due to the force exerted on the soft-magneticvalve body 3 by the permanent magnet PM the valve body is in contactwith the valve seat VS at a biasing force when the magnet coil 5 is notsupplied with an actuation current. When feeding an actuation current tothe magnetic coil 5 to thereby generate a magnetic field coacting withthe magnetic field generated by the permanent magnet PM, a force isexerted on the valve body 3 for displacing it a short distance,preferably about 0.1 mm, from the valve seat towards the coil 5 foropening the valve. As known per se in the art, the current fed to thecoil 5 has a pulse-like form having a pulse length of about 50microseconds for each generation of one drop.

A small amount of fluid becomes injected from the first chamber C₁ intothe second chamber C₂ due to the pressure difference between the fluidsF', F" in these two chambers when opening the valve by raising the valvebody 3 some tenths of a millimeter from its contact with the valve seatVS. At this moment, the pressure in the second chamber increases, sothat the process of forming a drop at the outlet formed by the nozzle 13begins.

When switching off the coil by interrupting the actuation current afterthe lapse of said pulse period, the valve body 3 moves back towards thethin partition wall PW. In this situation the partition wall is benteither due to a pressure-wave generated by the valve body's movementtowards the partition wall or generated by the physical contact of thevalve body with the partition wall. The bending of the partition walltowards the second chamber C₂ causes a pulse-like increase of thepressure of the fluid F" in the second chamber resulting in a completionof the forming of the drop at the nozzle.

FIG. 2 is a sketch for explaining the magnetic polarization resulting inthe desired actuation of the valve body 3. The coil 5 induces a desiredmagnetic field causing a polarization of the valve body 3. The magneticfield generated by the current through the windings of the coil 5 ischosen to have a polarity such that the free end of the valve bodybecomes the magnetic northpole and that its other end becomes themagnetic southpole. Hence, the valve body 3 becomes repelled by thenorth-pole of the permanent magnet PM being arranged close to the bottomend of the valve body 3. Thus, the valve opens. The pre-biasing of thevalve body for holding it in the closed position of the valve during therespecting resting phases can also be accomplished by using a coilspring (not shown here) instead of the permanent magnet for urging thevalve body in its closed position. Alternatively, a coil spring may beprovided for urging the valve body in its opened position instead of itsclosed position. In the latter case, the current fed to the actuationcoil 5 must be chosen to have an opposite polarity and must be generatedduring the respective resting phases, e.g. for holding the valve devicein its closed position.

Instead of using a solenoid valve device, other actuation devicesadapted for opening and closing the valve seat can also be used. Forexample, piezoelectric or magnetostrictive elements can be used insteadof the coil-valve body-actuation device.

FIG. 3 schematically shows the arrangement of a plurality of fluid jetprinting devices together forming an ink jet apparatus or ink jetprinter having 3×7 printing devices. These 21 fluid jet printing devicesA to U together form a column for forming 21 dots on a registrationmedium like registration paper passing by the nozzle. The circles A toG, H to N and O to U schematically designate the housing or centralportion of the respective printing devices. The fluid, preferably theink, is conducted through the ducts A₁₂ to U₁₂ of the respectiveprinting device to the associated nozzle A₁₃ to U₁₃.

The 21 fluid jet printing devices A to U have a common first duct plate10a as well as a common second duct plate 10b. Moreover, a single,common partition wall PW as well as a common stuffing foil 11 is usedfor all of the 21 printing devices. Consequently, a printer consistingof a plurality of fluid jet printing devices formed by a low number ofparts common to all of the printing devices is not only capable of ahigh frequency drop generation, but also has an extremely compactdesign.

I claim:
 1. A fluid jet printing device comprising:a first fluid chamberconnected to an inlet for feeding fluid into said first chamber, saidfluid within said first chamber being at a predetermined pressure; asecond fluid chamber having fluid therein at a pressure less than saidpredetermined fluid pressure in said first chamber and having a nozzle;a diaphragm-like partition wall having a valve seat and separating saidfirst and second chambers; a movable actuation member and a valve seatin combination forming a valve; means for selectively moving said memberaway from said wall to open said valve and inject fluid from said firstchamber into said second chamber and form a fluid drop at said nozzleand selectively moving said member toward and into contact with saidwall to bend said wall toward said second chamber and close said valveand increase the fluid pressure within said second chamber to furtherform said fluid drop and expel said fluid drop from said nozzle.
 2. Thedevice of claim 1 wherein said diaphragm-like partition wall has athickness within the range of 0.01 to 0.3 mm.
 3. The device of claim 1wherein said diaphragm-like partition wall has a thickness within therange of 0.02 to 0.05 mm.
 4. The device of claim 1 wherein said valveseat is a collar extending from an embossed hole in said diaphragm-likepartition wall.
 5. The device of claim 1 wherein said first fluidchamber includes a first plate having a plurality of said inlets andsaid second chamber includes a second plate having a plurality of saidnozzles, with a common partition wall interposed between said first andsecond plates.